This invention relates to a novel catalytic system useful in the conversion of organic nitro compounds to the corresponding organic isocyanates.
Organic isocyanates are used extensively in the preparation of urethane foams, fibers and coatings. Organic isocyanates also find use in the production of surface active agents, biocides, and the like.
Organic isocyanates have been prepared commercially from organic nitro compounds by a process which involves conversion of the nitro compounds to the corresponding amines and thereafter reacting the amines with phosgene. A newer and more efficient process permits the preparation of organic isocyanates directly from organic nitro compounds through a reaction with carbon monoxide at elevated temperatures and pressures in the presence of a catalyst. Appropriate catalyst systems that have been proposed have included noble metals, Lewis acids, and combinations thereof. A catalyst system comprised of a noble metal halide, a heteroaromatic nitrogen compound, and an component selected from the oxides of vanadium, molybdenum, tungsten, niobium, chromium and tantalum is disclosed in U.S. Pat. No. 3,576,835. In U.S. Pat. No. 3,674,827, it is suggested that further improvement in the recovery of organic isocyanates through use of such a catalyst system may be effected by the addition of discrete particles of iron oxide to the catalyst system.